Small Emperor Moth Facts

The Small Emperor Moth is a holometabolous insect found in regions all over Britain and Ireland, but it is most often associated with moorland and heathland areas. They have distinctive eye markings on their brown and white wings. Adult moths do not feed during the few months they are on the wing.

Appearing in April, the males fly in search of mates. With a wingspan ranging from 1.6 to 2.7 inches, brightly colored male Emperor Moths fly during the day while the females, muted in color, tend to appear at night.

Female Emperor Moths lay their eggs on a variety of different species of plants, including but not limited to: heather, meadowsweet, bramble, hawthorn and birch.

The young caterpillar appears orange and black at first and later grows to become green with rings of black, spotted with red and yellow. This species forms a fibrous cocoon in which it overwinters as a pupa.

The Family Saturniidae, Species and Subspecies

Saturniids belong to the order of Lepidoptera, which has an estimated number of species over two-thousand. This family contains some of the largest species of moth (like some Atlas moths with a wingspan up to 12 inches), and they are characterized by hair-like scales that cover their heavy bodies, small heads and mouths.

Although they lack a frenulum, their hind wings overlap the forewings to produce the effect of a conjoined wing surface. Male saturniids generally have larger and broader antennae, but all species show different forms of sexual dimorphism.

Most species of Saturniidae are found in wooded tropical and subtropical regions like Mexico. There are twelve documented species that live in Europe and sixty-eight documented species that reside in North America.

Small Emperor Moths are often mistaken to be small tortoiseshell butterflies, which are larger and belong to the family Nymphalidae. The Regal Moth, or Citheronia regalis, is one of the more easily handled caterpillars of the Saturniidae.

Saturniid caterpillars are usually ornate with vibrantly colored, sharp, stinging hairs. The caterpillars themselves can range in size from 2 to 4 inches and are stout and cylindrical in shape.

They feed on the foliage of shrubs and trees with the exception of the Hemileucinae subspecies that feed on grasses. Most saturniid larvae spin silken cocoons or burrow in small chambers underneath the soil.

There are eight subspecies in the Saturniidae family with the addition of one, Ludiinae, which is currently being disputed.These are the Oxyteninae, Cercophaninae, Arsenurinae, Ceratocampinae, Hemileucinae, Aglilnae, Salassinae, and Saturnilae.

Members of the subfamily Oxyteninae are primarily from Central and South America along with genera from Ceratocampinae. The Salassa Iola, a moth from the subspecies Salassinae, is a saturniid found in south-east Asia.

Saturnia Pavonia contains three subspecies: pavonia, which is found in southern Spain; josephinae, which is also found in southern Spain; and columbiana, which is found in Columbia and possibly Equador.

Small Emperor Moth Life Cycle – Egg Period, Larva, Pupa, Flight

The entire lifespan of an Emperor Moth can range from less than a year to three years or more. As an adult, the moth lives only a few months at most and usually averages about four weeks.

The Egg Period

During the months of May and June, eggs are laid by the female at night on food plants. If the moths reside near a higher-altitude environment such as hills, the adult selects birch, willow and heather plants to deposit her eggs.

In low-land areas, moths lay their eggs on bramble, blackthorn and meadowsweet. The small and black eggs are laid in batches of twenty, and they hatch at night approximately three weeks after being deposited.

Larva

The larvae of the Emperor Moth are small in size; furry, and black and orange in color. Molting several times in this stage, the caterpillar slowly increases its body mass to nearly 3,000 times its weight from egg to pupa by feeding exponentially each day.

Because the adult moth does not feed, it is imperative that the caterpillar eats as much as it can—both in order to complete metamorphosis and to ensure the longevity of its adult life.

The Emperor Moth caterpillar possesses powerful toothed jaws to help it chew through the foliage of its food plants. Upon hatching, the larvae are black with orange tufts of hair. As they grow, their coloration changes to bright green with black hoops that are speckled with yellow and red spots.

Pupa

Near the end of August, these herbivores can be found in the shrubs and undergrowth of their food plants as they prepare to pupate.

The process begins by the larva selecting a sturdy twig or stalk that is concealed sufficiently from potential predators.

Like most caterpillars, they do this by crawling back and forth on the stalk several times to test its durability and vantage point.

Once a suitable twig is selected, the larva spins a hardy, protective and mesh-like cover of various layers around itself with silk thread. The color of the cocoon varies from off-white to brown and is attached to the vegetation by a few threads of silk.

Predators are unable to enter it due to the shape of the entrance, which is formed with its narrow end facing outwards.

After the final larval instar, the pupa transforms into a violet-brown color. The soon-to-be moth remains in it during winter, sometimes taking up to three years to fully develop. This is in contrast to the four to six weeks that the moth requires to transition from the egg stage to pupa.

During the process of pupation, the cells in the body of the caterpillar slowly break down and regrow. At this point, the caterpillar’s internal organs are dissolved into a liquid state.

Once the the transformation is complete, the adult moth emerges from the pupa casing and hauls itself onto a branch nearby in order to pump blood into the wing.

Adult

The wings of the adult Emperor Moth display four spots in order to intimidate possible predators. From a distance, these spots appear to resemble cat eyes.

These moths are also known to rapidly flutter them when under threat. Although the Emperor Moth is sometimes mistaken for the smaller Eyed Hawk Moth, the Eyed Hawk Moth only features two eye-spots on its hind wings.

The body of the Small Emperor Moth is covered with fur and its wingtips are colored with pinkish-red markings. Adult males are smaller but their colors are more vivid.

They have orange hind wings while the females (sometimes referred to as the “night butterfly”) are muted and gray in color.

By resting throughout the day, the adult females emit pheromones to signal their position and attract possible mates. Several males will surround around one single female until one of the adult males mates with her.

Adult moths are on the wing from April to early June. Emperor moths of both sex fly in a zigzag pattern on open ground, but females fly slower in comparison to the males.

Since adult males fly during the daytime, they pick up the pheromones with their (often larger) feathery antennae from over several miles away.

Habitat

The Small Emperor Moth prefers open scrub habitats, but it is well-adapted to both high and low altitudes. The moth is found primarily in heathland, moorland bogs, hedgerows, sand dunes, field margins, fens and woodland rides.

They are well distributed throughout the United Kingdom, the Channel Islands, the Scottish Western Isles and the British Isles. Many sightings have been made at Eastern Cliff Kennack Sands on the Lizard Peninsular, Cornwall.